The present invention relates to photonics chips and, more specifically, to structures that include a waveguide and methods of fabricating a structure that includes a waveguide.
Photonics chips are used in many applications and systems including, but not limited to, data communication systems and data computation systems. A photonics chip integrates optical components, such as waveguides and bends, and electronic components, such as field-effect transistors, into a unified platform. Layout area, cost, and operational overhead, among other factors, may be reduced by integrating both types of components on a single photonics chip.
The optical components of a photonics chip may be fabricated by patterning the semiconductor material of the device layer of a silicon-on-insulator wafer. The electronic components of a photonics chip may be fabricated by front-end-of-line processing using the semiconductor material of the device layer of the silicon-on-insulator wafer. A dielectric layer stack is deposited over the optical components prior to the formation of the middle-of-line and back-end-of-line interconnect structures. The dielectric layer stack includes a layer of silicon nitride that forms a continuous and unbroken slab over a region containing the optical components, a region containing the electronics components, and a transition region between the region containing the optical components and the region containing the electronics components. The silicon nitride in this slab incorporates hydrogen that, through nitrogen-hydrogen bonds, introduces absorption of the optical signals propagating in the optical components. An unwanted consequence is optical signal loss in the optical components from the overlying silicon nitride, which may be undesirable for long-range routing of the propagating optical signals.
Improved structures that include a waveguide and methods of fabricating a structure that includes a waveguide are needed.